Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Becerro, A. I. Articles by Mantovani, M.

The hydrothermal conversion of kaolinite to kalsilite: Influence of time, temperature, and pH

¹ Instituto de Ciencia de Materiales de Sevilla-Departamento de Química Inorgánica (CSIC-US), 41092 Sevilla, Spain
² Bayerisches Geoinstitut, Universität Bayreuth, 95440 Bayreuth, Germany

Correspondence: ^* E-mail: anieto{at}icmse.csic.es

Kalsilite (the low-temperature form of KAlSiO₄) is used as the precursor of leucite, an important component in porcelain-fused-to-metal and ceramic-restoration systems, and it has also been proposed as a high-thermal expansion ceramic for bonding to metals. The present study reports the hydrothermal synthesis and characterization of pure kalsilite from kaolinite in subcritical conditions, as well as the characterization of the intermediate products by means of XRD, ²⁹Si and ²⁷Al MAS NMR, IR, SEM, and TEM. Effects of time, temperature, and pH on the reaction products are analyzed. The experimental data indicate that pure kalsilite is obtained after hydrothermal treatment of kaolinite at 300 °C for 12 h in 0.5 M KOH solution. Longer reaction times increase the crystallinity of the structure, whereas lower reaction times give rise to the metastable ABW-type KAlSiO₄ polymorph. Lower temperatures are not sufficient to produce kalsilite, but zeolite W is obtained instead as the unique reaction product. Finally, the pH of the aqueous solution in contact with kaolinite is an important parameter for the synthesis of kalsilite, which must be 13.70.

Key Words: Kalsilite • kaolinite • hydrothermal synthesis • MAS NMR • XRD